GRAPEVINE October 2013 - 7
Fresco Painting:
The Preparation of the Substratum
The second of a three-part article by Julia Alexandra Mee
T
he term 'fresco' means 'fresh',
and refers to painting on wet,
that is, 'fresh’ plaster. The
pigments (those which support
the alkalinity of the plaster) are ground
into powder, and mixed in water, lime
water or lime milk, and are applied onto
the surface whilst it is still moist.
Subsequently, as the calcium hydroxide
(slaked lime) is exposed to the carbon
dioxide in the air, it is transformed into
calcium carbonate, fixing the colours
within a durable surface, a process which
is known as carbonatisation (Ca(OH)2 +
CO2 = CaCO3 + H2O).
In buon affresco ('vero' fresco), the
preparation of the wall consists of the application of a number of layers of rendering. Over the centuries, the thickness of
the ground used in fresco painting has varied. In the ancient wall paintings discovered during the excavations at Herculaneum and Pompeii, at least seven or
eight layers of rendering had been applied, whilst during the Renaissance as
few as two or three were employed.
The first layer of rendering, known as il
rinzaffo (il trullissatio or scratch coat), is
applied onto the surface of the wall (which
is preferably of bricks or stone) to regularise any irregularities and holes that are present.
The mortar is composed of slaked lime and clean
river sand of a very large grain (or more traditionally, fragments of terracotta or pozzolana). This
rendering is left to dry out completely before the
second layer is applied, the so-called arriccio
(incrostature or sand coat), which is formed of a
mortar of slaked lime and clean river sand of a
large grain. The entire compositional drawing
known as the sinopia (after the red sinoper pigment used in the process) is executed on this
layer. When this has completely dried out, the
intonaco is applied (the layer to be painted),
which is composed of slaked lime mixed with
clean river sand of a finer grain or marble powder,
upon which the painting is executed. This was
sometimes followed sometimes by a thinner
layer known as the intonachino or velo, which
contains slightly more lime in the mortar.
The renderings are applied in progressively
thinner layers, with more lime added to the mortar with each successive layer, and the use of
sand or marble powder of a progressively finer
grain. The last layer of rendering, the intonaco
(and if present the intonachino), is applied in relatively small sections which have been predetermined according to the composition of the
drawing. At the beginning of the day, one section of intonaco is applied which is large
enough to be painted and completed before the
plaster becomes too dry at the end of the working day, hence the term giornata (from the
Italian word 'giorno' meaning 'day').
According to the Roman writer, architect
and engineer Marcus Vitruvius Pollio, who
recommended at least seven layers of rendering in his influential De Architectura
(c.15 BC), there should be at least one layer
of rinzaffo, three of arriccio, and three of
intonaco. This contributed towards a greater
reserve of moisture in the ground, which allowed more time for the painting process,
and as a result the intonaco was applied in
pontata (large sections of plaster which corresponded to the scaffolding), examples of
which can be seen in the wall paintings in
Herculaneum and Pompeii. In later centuries, such as in the Renaissance, fewer layers
were applied, sometimes only one of
arriccio, upon which the drawing was executed, and one of intonaco. Consequently, it
was necessary for the intonaco to be applied
in smaller sections (in giornate), since there
was less time at the artists' disposal for the
painting process.
All of the works of art reproduced here are
by Julia Alexandra Mee.
1
2
3
In November: Fresco Painting, The Painting
Process.
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Click here to read an article from last month: >>
1. Fresco demonstration panel of Una Giovane Donna, sinopia.
2. Fresco demonstration panel of Una Giovane Donna (1911), following the Renaissance technique.
3. Fresco demonstration panel of Un Ritratto di un Giovane Uomo following the technique described
by Vitruvius.
4. On the left, the full-size drawing for Il Chitarrista, and on the right (5), the use of the pouncing
technique to transfer the drawing from the spolvero onto the arriccio. Il Chitarrista was painted
at the Villa San Rocco Studio, Benabbio, in 2012.
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5